The present invention relates to a process for the steam cracking of hydrocarbons. It also relates to an improvement in the steam cracking of hydrocarbons whereby reduced coking and carbon monoxide formation is observed.
Steam cracking of hydrocarbons is mostly used for olefins production. It is known that pyrolytic coke is formed and deposited on metal surfaces in contact with a hydrocarbon feedstock undergoing pyrolysis (i.e. high temperature thermal cracking). The consequences are (i) that the heat flux to the hydrocarbons is reduced and (ii) that the pressure drop across the reactor increases. Thus, the reactor operation has to be stopped periodically to remove the coke (said removal being usually carried out by burning the coke).
Further, the steam which is added as a diluent in steam cracking can react with the hydrocarbons in reforming reactions, catalyzed by the metal of the reactor, leading to the formation of substantial amounts of carbon monoxide. The latter is an unwanted component in the product, as it reduces the yield of valuable products and behaves as a poison towards many catalysts used in downstream reactions.
It is known that sulphur compounds inhibit said reforming reactions and thus the formation of CO, and it has therefore been proposed to add various sulphur compounds, of which dimethyldisulphide (DMDS) is most frequently used.
The feedstocks used in the steam cracking of hydrocarbons contain natural sulphur. Even with the addition of further sulphur compounds, the results were still not satisfactory in terms of the combination of reduced coking rate and reduced carbon monoxide formation.
It is thus an object of the present invention to provide a process for the steam cracking of hydrocarbons having a reduced coking rate.
Another object of the invention is to provide a process for the steam cracking of hydrocarbons yielding lower yields of carbon monoxide.
A further object of the invention is to provide a process for the steam cracking of hydrocarbons combining a reduced coking rate and lower yields of carbon monoxide.
Yet another object of the invention is to provide a process for the steam cracking of hydrocarbons while avoiding steam reforming reactions.
Still another object of the invention is to provide a process for the steam cracking of sulphur-containing hydrocarbons having one or more of the above advantages.